With miniaturization in an integrated circuit of a semiconductor, an interlayer insulating film called a “low-k layer” for lowering a dielectric constant has been required. However, since the low-k layer has a void structure, a problem arises that mechanical strength is lowered. In order to protect an interlayer insulating film having such a weak mechanical strength, a cured film formed of a polyimide resin is used. This cured film is required to have properties such as capability of being thick and having a high modulus elasticity. However, due to an increase in thickness and an increase in modulus elasticity, the stress after curing may increase, and problems may arise that transfer or securing of a wafer may not necessarily be conducted smoothly due to significant warpage of a semiconductor wafer. Under such circumstances, development of a cured film having a low stress has been desired.
In order to allow a cured film to have a low stress while keeping high thermal resistance and excellent mechanical properties of a polyimide resin, it has been reported that it is effective to decrease the coefficient of thermal expansion by allowing the polyimide skeleton to be rigid and linear.
Further, if a resin film is formed to have a large thickness in view of protection of a low-k layer, there is a problem that the transmittance of i-line that is used for forming a pattern in a resin film is lowered, and as a result, formation of a pattern becomes impossible. On the other hand, in order to increase i-line transmittance of a coating film, a method has been proposed to use a polyimide precursor containing fluorine.
However, there is a disadvantage that a cured film obtained by curing by heating a polyimide precursor containing fluorine has low adhesiveness to silicon wafer used as a substrate (Patent Documents 1 and 2, for example).
Further, in order to attain excellent adhesiveness with silicon wafer, use of 3-isocianatopropyltriethoxysilane as a resin composition has been reported (Patent Document 3, for example). However, there is a problem that the storage stability of the resin composition is lowered due to the presence of an isocyanate group having a high reactivity.